Kites of various shapes, sizes and configurations are well-known in the art. The vast majority of kite designs achieve lift through one or more stationary planar surfaces pulled by a string at a positive angle of attack relative to the wind.
Some of the kites found in the prior art include rotating surfaces. Rotating surfaces are typically incorporated primarily either for novel and amusement reasons or as a means for generating lift. U.S. Pat. Nos. 2,074,327 and 3,514,059 are examples of the former category, employing very large planar surfaces which rotate primarily for amusement purposes.
In the latter category, a rotor or propeller is typically employed as the rotating surface. In rotorcraft there exists a substantial lateral or roll stability problem due to asymmetric lift of the blades of the rotor. When subjected to a relative wind from a forward direction, a forward-moving blade experiences an increase in the speed of air flowing across its surface equal to the relative wind. Conversely, a rearward-moving blade experiences a decrease in the speed of air flowing across its surface equal to the relative wind. The result is that the forward-moving blade generates more lift than the rearward-moving blade, causing a tendency to roll in the direction of the rearward-moving blade.
Various approaches have been attempted to control this lateral stability problem. For example, some prior art designs have employed a pair of oppositely arranged propellers or rotors to effectively cancel out the tendency towards rolling (see U.S. Pat. Nos. 2,472,290 and 2,987,280). Other approaches which have been attempted include employing a large horizontal stabilizer to counter the rolling tendency or a yoke with a tether attached at opposite lateral ends (see U.S. Pat. No. 3,727,864).
Yet another approach is illustrated by U.S. Pat. No. 3,194,521. In this design, the blades of the rotor are independently hinged about a hub, thereby allowing a forward-moving blade to rotate upwardly in response to a forward relative wind. However, this approach is relatively complicated and expensive to manufacture, requiring numerous parts and a complex resilient section on the inner portion of each blade in order to achieve aerodynamic roll stability.
What has been needed is a simple, low cost, easy to manufacture, tethered model gyroplane which overcomes the aerodynamic lateral stability problems associated with rotorcraft.